The major objectives of the grant proposal involve the study of plasma membrane receptors for growth hormone, prolactin and insulin, with particular emphasis on prolactin. Studies in prostate and testes, kidney and liver slices, human mammary tumors, and human liver will be carried out. The autoregulation of the prolactin receptor will be examined. In order to understand the interaction of prolactin and growth hormone with their receptors, studies on the solubilization, purification, and characterization of both the prolactin and growth hormone receptors will be undertaken. A second major objective is the study of non-primate placental lactogens in the rat, sheep, goat and cow. Purification and characterization studies are underway. The nature and significance of a specific growth hormone binding factor identified in pregnant mouse serum will be explored. A third objective is to continue to examine the role of human prolactin in health and disease. BIBLIOGRAPHIC REFERENCES: B. I. Posner, P.A. Kelly and H.G. Friesen. Prolactin Receptors in Rat Liver: Induction by Prolactin. Science 188:57-59, 1975. P. Hwang, H. Guyda and H.G. Friesen. Purification of Human Prolactin. In: Methods in Enzymology 37: Hormone Action Part B Peptide Hormones ed: B.W. O'Malley and J.G. Hardman, Academic Press, New York, pp. 389-402, 1975.